Tertiary oil recovery method



NOV. 1968 W E BRlGHAM ET AL 3,410,341

TERTIARY OIL RECOVERY METHOD Filed May s. 196e 4 sheets-sheet 1 /f-f diff W..

illllllllll 0 1 IIIIIg INVENTORS WILLIAM E. BRIGHAM JOHN N. DEW

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A TORNE Y 4 Sheets-Sheet 4 W. EV BRIGHAM ET AL TERTARY OIL RECOVERYMETHOD Nov. 12, 1968 Filed May 5.

HBAOSH IO .LNBO 83d INVENTORS WILLIAM E. BRIGHAM JOHN N. DEW BY MOE/73?M Ar olW/ fy` UnitedStates Patent O 3,410,341 TERTIARY OIL RECOVERYMETHOD William E. Brigham and John N. Dew, Ponca City, Okla., assignorsto Continental Oil Company, Ponca City, Okla., a corporation of DelawareFiled May 5, 1966, Ser. No. 547,843 13 Claims. (Cl. 166-9) ABSTRACT OFTHE DISCLOSURE A tertiary recovery process for improving t-he recoveryof oil from a reservior which has been 'waterflooded Said processcomprises injecting a material which is somewhat soluble in water andmore soluble in the reservoir oil, injecting a second material which ismiscible with said rst injected material, and injecting a third materialwhich is miscible with said second injected material and which acts as adrive fluid to drive said oil through the reservoir and through aproducing well in communication with said reservoir.

This invention relates to a method for increasing the recovery of oilfrom reservoirs. In one aspect, it relates t-o a tertiary recovery ofhydrocarbons following a water ilood by a method of combined oodingmedia, which is novel and unique in the art, in order that substantiallyall the oil in a reservior may be recovered.

In recovery of oil from oil reservoirs, several methods have beenproposed for increasing the recovery of the oil in place in thereservoir. Among these proposals has been the injection of Watercommonly referred to as waterflood, the injection of normally gaseoushydrocarbons, the injection of a 100% pore volume of propane, theinjection of propane followed by water, and the injection of a slug ofImiscible fluid followed by a hydrocarbon gas. The foregoing methods ofrecovery are commonly referred to as secondary recovery operations inthat they are recovery efforts which are applied in order to obtainproduction subsequent to the economic vproduction obtainable byutilizing naturally occurring energy or conventional pumping means. Theuse of miscible fluids in secondary recovery operations is known in theart, particularly the injection of low molecular weight normally gaseoushydrocarbons. Methods utilizing such :hydrocarbons are extremelysuccessful with regard to the displacement efficiency of thehydrocarbons, particularly the ability to displace essentially all ofthe Ihydrocarbons from the formation, but the volumetric efficiency ofthis ilooding media is a disadvantage. The hydrocarbons inherentlylinger and channel to -a great extent and a large portion of thereservior is bypassed though the volume of injected hydrocarbons may begreat. This brings up the further disadvantage of expense per volume andinability to obtain suflicient volumes of the ooding media. Thesedisadvantages are particularly prevalent when miscible iiooding isattempted on a reservoir which has been previously waterooded. Thisadditional flooding following waterood operations has been termedtertiary ilooding. Miscible flooding has been found to be veryinefficient for displacing oil after a waterflood. For instance,recovery of oil by miscible flooding following a secondary waterfloodingoperation typically recovers only about 30% or less of the oil -inplace.

A typical miscible ooding process is the miscible slug process. Ineffect this is a liquid-liquid miscibility process which consists ofinjecting a limited quantity of propane, LPG, or similar solvent into anoil reservoir and pushing this liquid bank toward producing wells withsubsequently injected gas. The injected liquid being miscible withreservoir oil results in eicient displacement of the oil. The process inessence consists then of both 3,410,341 Patented Nov. 12, 1968 "iceliquid-liquid and gas-gas miscibility. Miscibility can be explained asthat p'hysical condition between two liquids that will permit them tomix in all proportions without an interface being formed by thematerials. If the two iiuids do not mix in all proportions, they .areimmiscible.

After waterooding any reservoir the remaining oil is typically presentas immobile oil droplets surrounded by a layer of water; therefore, whenmiscible flooding is attempted following a waterflood, the propane orUPG solvent is unable to make contact with the oil droplets and thusresults in an inefficient recovery of oil from the reservoir.

An object of this invention is to provide an improved process forrecovering oil from .a reservoir which has been waterooded.

Another object of this invention is to provide a process by which oil israpidly recovered from a reservoir which has been watertlooded.

A further object of this invention is to provide an improved miscibleooding process which is suitable for re covering oil from a reservoirwhich has been waterflooded.

An additional object of this invention is to provide an improvedtertiary recovery process which overcomes and avoids the disadvantagesof the prior art.

`Other objects and advantages of the present invention will becomeapparent from the following detailed description of the invention.

The foregoing objects are achieved by an improved miscible floodingoperation following a waterflooded. This improvement comprises, afterwaterflooding initially, injecting a material which is somewhat solublein water and more soluble in the reservoir oil. Said material isfollowed by a typical miscible solvent, such as propane or LPG, which inturn is followed by a miscible gas to drive the oil through thereservoir. By miscible gas we mean a gas miscible with the misciblefluid immediately ahead of said gas. It is believed that the initiallyinjected material, being slightly soluble in water, penetrates the waterlayer and, being considerably more soluble in oil, tends to increase thevolume 'occupied by the immobile oil particles thereby making the oilmobile and capable of forming an oil bank ahead of the miscible tiood.This process results in an increased recovery of oil from the reservoirin a shorter period of time than is possible without the injection ofthe initially injected material.

As stated previously, the material which is injected into the reservoirprior to the injection of the miscible fluid is a material which issomewhat soluble in water and more soluble in the reservoir oil. Thismaterial'can be carbon dioxide, aliphatic alcohols, -ketones, aldehydes,acids and esters. These aliphatic materials typically have a solubilityin water of about 5 to about 2() grams per milliliters at 20 centigrade.Some specic materials in addition to CO2 'which have been found suitableinclude: l-butauol, 2-biutanol, 2-pentanol, 2-methyl-2-bu tanol,propanol, 3-pentanone, butanoic acid, methyl propanoate, and ethylethanoate. The quantity of this material which is added to the reservoiris dependent upon the quantity of miscible fluid which is subsequentlyadded and is normally about 1 to 10 percent of the miscible fluid added.Typically the amount of first-injected illuid will be between about.0005 and about .02 hydrocarbon pore volumes.

The miscible fluid which is added to the reservoir following theaddition of the first-injected material is a fluid which is misciblewith the reservoir oil. The miscible fluid can include ethane, propane,butane and LPG. LPG, as is well known, consists principally of propanewith minor proportions of pentane and normally a very small amount ofethane. The quantity of miscible uid added to the reservoir depends uponthe particular reservoir involved but typically varies between about .05and about .20 pore volumes.

The miscible gas which is injected into the reservoir following theinjection of the miscible fluid is a gas which is -miscible with themiscible fluid previously added. This miscible gas can be natural gas,liuc gas, nitrogen and other inert gases. The `quantity of imiscible gasadded to the reservoir is dependent upon the reservoir; however, the gasis normally injected in suici'ent quantities to drive the reservoir oilthrough the reservoir and thereafter through a producing well.

The order of injection of materials into the reservoir according to thisinvention is the material which is somewhat soluble in water and moresoluble in reservoir oil, followed by the 'miscible uid, which in turnis followed by the miscible gas. In addition, it has been found that theinjection of small slugs of water with small slugs of each injectedmaterial gives an improved result in some reservoirs. For example,alternate slugs of CO2 and water are added until the desired amount ofCO2 has been added, butane and Water slugs are alternately added untilthe desired quantity of butane is added, then alternate slugs of naturalgas and water are added until the producing wells reach their economiclimit.

The method of the present invention is adaptable to application to anyhydrocarbon-bearing reservoir blut most readily on a field-wide basiswherein the reservoir is traversed by several `well bores. The wells maybe arranged in a conventional manner such as a five spot or linepattern, or as the individual situation demands, with certain of thewells being used for the injection of the displacement media and othersfor recovery of the hydrocarbons.

Prior to the application of this method to a reservoir, it is necessaryto have certain data on the reservoir which is readily determinable byprocedures -known in the art: such as, effective oodable pore volume ofthe formation, average interstitial water saturation, applicablerelative permeability characteristics, and amount of displacementhydrocarbon required to maintain miscibility between the reservoir oiland the displacing gas during the life of the flood.

In order to more fully describe the invention, reference is made to thedrawings of which: l

FIGURE 1 represents a reservoir which has been previously waterflooded.

FIGURE 2 represents a reservoir which has been previously waterooded andsubsequently treated in accordance with this invention.

FIGURE 3 is a graph representing a Berea sandstone core which has beenflooded with butane in one instance and waterflooded prior to butaneflooding in another instance.

FIGURE 4 is a graph showing a Berea sandstone core which has beenwaterflooded prior to being treated with butane in one instance andwaterflooded followed by butyl alcohol and subsequently flooded withbutane in another instance.

FIGURE 5 is a graph showing a Berea sandstone core which has beenwaterllooded followed by butane in one instance and waterooded followedby CO2 followed by propane in another instance.

Referring to FIGURE 1 of the drawings, a subterraneanhydrocarbon-bearing formation is traversed by an injection well 1 and aproduction well 3. Oil droplets 5 surrounded by a layer of water 4result from previously waterooding reservoir 15. These oil droplets areshown in an enlarged form for ease of illustration. The oil droplets,which are formed during the waterflooding operation, are present in animmovable form and are, therefore, not susceptible to treatment byordinary miscible ooding to any great degree.

In FIGURE 2 of the drawing, a subterranean hydrocarbon-bearing formation15 is traversed by aninjection well 1 and a producing well 3. A material9, which is somewhat soluble in water and more soluble in the reservoiroil, is injected through injection well 1. A miscible fluid 11 ininjected following injection of material 9. A miscible gas 13 isinjected following injection of miscible uid 11. An oil bank 7 is builtup by material 9 acting upon oil droplets 5. This bank of oil issubsequently swept through the reservoir and produced as oil throughproducing well 3. The various lines are shown in FIGURE 2 representingthe materials added as interfaces between each material; however, thisis done merely for ease of illustration and it must be understood thatthese are not interfaces in the true sense but are transition zonesvarying from one end of the zone as a zone rich in hydrocarbon oilthrough the other extreme zone which is rich in miscible gas. This isthe typical situation which is present in miscible flooding. Thematerial represented by numeral 9 in FIGURE 2 can be carbon dioxide orcertain aliphatic alcohols, aldehydes, ketones, acids and esters whichmeet the solubility requirement previously stated.

Referring to FIGURE 3 of the drawing, it can be seen that a Bereasandstone core treated with a butane flood removes essentially all ofthe included oil with the injection of approximately 2 pore volumes.This `ligure also shows the treatment of the Berea core with awaterilood followed by butane. As can be seen from the figure, only 40%of the oil is recovered by the waterflood and with the addition ofbutane at 2 pore volumes only about 72% of the hydrocarbon has beenrecovered.

Referring to FIGURE 4 of the drawing, a Berea sandstone core is treatedin one instance with a waterood followed by butane with the resultingrecovery at any given `pore volume of less oil than can be obtained withthe addition of butyl alcohol following the waterflood and subsequentlya 1butane ood. For example, at 2.5 hydrocarbon pore volumes injected thewaterood followed by butane gives approximately 77% recovery whereas theWaterilood butyl alcohol and butane system at 2.5 pore volumes gives arecovery -of approximately 88%.

Referring to FIGURE 5 of the drawing, a Berea sandstone core is treatedwith -waterllood followed by butane and the resulting recovery at 2 porevolumes is approximately 73% Whereas the waterood-COZ-propane systemgives approximately 88% recovery at 2 pore volumes injected. It shouldbe noted that in this system butane is used in one instance and propanein the CO2 system. The difference between results at 2 pore volumeswould ybe even greater had CO2 propane Ibeen compared with the propanesystem, it being known that butane has a tendency to recover a greaterpercentage of oil than does propane.

In -order to more fully disclose and teach the invention, the followingexamples are included by way of illustration.

Example I A Berea sandstone core lwas saturated with oil. Butane waspassed through the core and percent oil recovered was compared againsthydrocarbon pore volumes injected. At 2.0 pore volumes injected, of theoil was recovered. This core was again saturated with oil. The core waswaterooded to recover about 40% of the oil. Butane was then added andthe percent oil recovered was compared to the pore volume injected at2.0 pore volumes injected, only 72% of the oil was recovered. Thisexperiment shows the effect of a prior waterfiood on the resultso-btained by miscible flooding. The results of this experiment are shownin FIGURE 3.

Example II A Berea sandstone core was saturated with oil. The core waswaterooded and then butane was injected. Percent oil recovered wascompared with pore volume injected. At 2.5 pore volumes injected, 77% ofthe oil -was recovered. This core was then cleaned and saturated againwith oil. The core was waterooded, 0.1 pore vvolumes of butyl alcohollwas injected and butane was added. Percent oil recovered was comparedwith pore volumes injected. At 2.5 pore volumes injected, 88% of the oilwas recovered. This experiment shows the improvement obtained whenalcohol is injected prior to miscible flooding. The results are shown inFIGURE 4.

Example III A Berea sandstone core was saturated with oil. The core waswaterooded and then butane was injected. Percent oil recovered wascompared with pore volume injected. At 2.0 pore volumes injected, 73% ofthe oil was recovered. This `core was then cleaned and saturated againwith oil. The core was waterooded, 0.1 pore volurnes of CO2 was injectedand propane was added. Percent oil recovered was compared with porevolumes injected. At 2.0 pore volumes injected, 88% of the oil wasrecovered. This experiment shows the improvement obtained when CO2 isinjected prior to miscible flooding. The results are shown in FIGURE 5.

Example IV A conventional five-spot well pattern covering 40 `acres andlocated in the Sussex ield in Johnson County Wyo., traversed theoil-bearing Lakota sand formation at a depth of approximately 7,200feet. This reservoir has Ibeen previously waterllooded. The formationtemperature is 180 F. and pressure is 2200 p.s.i. The method of tertiaryrecovery of the present invention could most readily be applied to theportion of the reservoir encompassed within the area of the pattern byutilizing the center well as the injection well and the remaining fourperipheral wells, at an average distance of about 933 feet from theinjector, as recovery wells. The formation sand, having a thickness offeet, has an average porosity of 14 percent, an average permeability of110 md., and saturations as follows: interstitial water of 54 percent,reservoir oil of 4l percent, and reservoir gas of 5 percent.

Determinations by known methods based on the foregoing data indicate thepore volume of the formation would be 434,000 barrels, ycontainingapproximately 178,000 barrels of reservoir oil which is subject torecovery by the present method. The `amount of CO2, propane and naturalgas necessary to effect recovery would be .002, .05, and approximately3.0 pore volumes respectively; so 62 tons of CO2 which is 868 barrels atreservoir conditions, 21,700 barrels of propane and approximately 350MMof s.c.f. of natural gas (essentially methane) are injected in thatorder. The volume of natural gas injected is only approximate since theactual volume injected will depend on when the producing wells reachtheir economic limit.

The recovery of such a `iield situation would effect the production of107,000 barrels of the reservoir oil in place after waterooding or 60%It `will be understood that the examples included herein areillustrative only and that the invention is to `be taken as limited onlyby the scope of the appended claims.

What is claimed is:

1. A tertiary recovery process following a waterflood for increasing therecovery of oil from a subterranean reservoir having in communicationtherewith :at least one injection well and one production wellcomprising:

(a) Injecting into said reservoir through said injection well an amountequal to between about .0005 and about .02 hydrocarbon pore volumes, aslug lof a material which is somewhat soluble in water and more solublein reservoir oil, said material being selected from the group consistingof `carbon dioxide and aliphatic alcohols, aldehydes, ketones, acids andesters, said aliphatic materials having a solubility in water of about 5to about 20 grams per 100 milliliters at 20 C.; n

(b) Thereafter injecting into said injection Well 1n an amount equal tobetween about .05 and about .20 hydrocarbon pore volumes, a fluidmiscible with said reservoir oil;

(c) Thereafter injecting into said injection well in quantities suicientto drive the reservoir oil through said reservoir and thereafter throughsaid producing well, a gas miscible with the miscible uid of step- (lb);and

(d) Alternately injecting small slugs of water with small slugs of eachinjection of said material of paragraph (a), said miscible fluid ofparagraph (b) and said miscible gas of paragraph (c) until the desiredquantity of each lmaterial has been added.

2. A process as recited in claim 1 wherein said rst injected material iscarbon dioxide, said miscible uid is selected from the group consistingof LPG, ethane, propane, and butane, and said miscible gas is an inertgas selected from the group consisting of natural gas, ue gas andnitrogen.

3. A process as recited in claim 1 wherein said rst injected material isl-butanol, said miscible fluid is butane and said miscible gas isnatural gas.

4. A process `as recited in claim 1 wherein said first injected materialis carbon dioxide, said miscible fluid is propane and said miscible gasis natural gas.

5. A process as recited in claim 1 wherein said rst injected material iscarbon dioxide, said miscible fluid is ybutane and said miscible gas isnatural gas.

6. A process as recited in claim 1 wherein said rst injected material isZ-butanol.

7. A process as recited in claim 1 wherein said first injected materialis Z-pentanol.

8. A process as recited in claim 1 wherein said first injected materialis 2methyl-2butanol.

9. A process as recited in claim 1 wherein said first injected materialis propanol.

10. A process as recited in claim 1 wherein said first injected materialis 3-pentanone.

11. A process as recited in claim 1 wherein said first injected materialis butanoic acid.

12. A process as recited in claim 1 wherein said irst injected materialis methyl propionate.

13. A process as recited in claim 1 wherein said first injected materialis ethyl ethanoate.

References Cited UNITED STATES PATENTS 3,033,288 5/1962 Holm 166-93,131,759 5/1964 Slusser et al.

3,249,157 5/1966 Brigham et al. 166-9 3,262,498 7/ 1966 Connally 166-9OTHER REFERENCES Holloway, Performance of a Miscible Flood WithAlternate Gas-Water Displacement, Journal of Petroleum Technology, April1964 (pp. 372-376).

Talash et al., Miscible Displacement After Waterilooding, The PetroleumEngineer, September 1957 (pp. yB-27 to B-30) STEPHEN I. NOVOSAD, PrimmyExaminer.

